The present invention relates to a thread guide structure for circular knitting machines, in particular for line-forming, units in double-cylinder machines for manufacturing socks and stockings.
As is known, in double-cylinder circular knitting machines the thread is fed to the needles of the machine by sets of thread guides, also known as line-forming units, which are arranged at each feeding station of the machine laterally to the needle cylinders. In known line-forming units, each thread guide can be actuated individually in order to pass from an inactive position, wherein its thread dispensing end is spaced from the needle cylinders so as to prevent the needles from engaging the thread, to an active position, wherein the thread dispensing end is moved closer to the needle cylinders in order to allow the correct feeding of the thread to the needles.
By means of line-forming units it is possible to feed, to a same feed of the machine, threads having different colors, counts and components, so as to meet the various production requirements.
The passage of each thread guide from the inactive position to the active position is obtained with various types of actuation device which cause an oscillation of the thread guide about an axis which is parallel to the axis of the needle cylinders and subsequently a translatory motion of the thread guide toward the needle cylinders.
In some kinds of knitting it is necessary to feed the machine with two or more thread guides of a same line-forming unit; in order to allow the needles to correctly engage the threads, the thread delivery ends of said thread guides must be extremely close to each other in the active position.
Furthermore, in some cases the thread guide which is subsequently actuated must pass over a thread guide which has been actuated previously and is thus already in the active position.
In order to achieve this effect, the line-forming unit is provided, on the opposite side with respect to the needle cylinders, with a plate in which an appropriate path is defined; the thread guide engages said path so that, in moving from the inactive position to the active position, or vice versa, it follows said path and thus does not interfere with any thread guide which might be already in the active position. The use of plates in which thread guide paths are defined complicates the manufacture of the line-forming units and the calibration of the thread guides. Furthermore, precision in the actuation of the thread guides decreases in the course of time due to the unavoidable wear of said plates.
Another problem which can be observed in the use of these plates is linked to the increase in bulk which they entail in the line-forming units in a region of the machine where space problems are particularly important.